Thomas thorp



1 f (Nh noden) I l -f y .l T.TH0RP. A OPTICAL INSTRUMENT FR TESTING DIAMONDS., f

NO- 574.588.` y PatentedJan. 5,1897. 5

I `,Qwest l' l I Inn/enfer 4 1 1 /0 nM/@6d l.; figg @MKV/2% UNITED 'rnonas 'moan or WHITE-FIELD, ENGLAND. f

SPECIFICATION forming part of Letters Patent No. 574,588, dateclvJ'anuaiy 5, 1897. -v

Application led July 20, 1895.

To all ulmm. il muy concer/L.-

3e it known that I, T HOALAS Tuokl, a sub- Iiectof the Queen of Great Britain, anda resi dent; of 'hitefield, near \Ianehester, in the.

county of Lancaster, England, have invented certain new and useful Improvements in Optical Instruments for Testing Diamonds, of which the following is a specificati ion.

This invention consists in the construction of an optical instrument having for its object the testing of cut diamonds and the detection of imitation diamonds or paste" when ent and set as brilliants.

The construction of the said instrument is based upon the following optical principles:

As is well known among physicists, when light passes from one refractive medium to :mother possessing greater ref raetive properties some of. the light incident upon the latter medium is reflected into the former and renders the form of the reflecting-surfaces visible when looked at through the former medium. 'here light passes from one medium to another having the same refractive power, no lightJ is reflected, but all is transmitted through the second medium, which is thus invisible when looked at through the fiIst.

In the ease where light passes from a higher to a lower refractive medium there is an aui but all is reflected into the higher medium,

and prisms of glass whose angle exceeds the critical angle are known as totalLv-retlect-V ing" prisms.

The improved instrument based upon the i principles stated above is shown on the drawings in two moditied forms of construction.

Figure 1 shows au end view, and Fig. 2 a

sectional side view, of the same; Figs. 3 and .4, similar views of a modified form thereof.

lu carrying out Iny invention l make use of a reflecting-prism, a totally-reflecting one Serial Ho. 556,573. No model.)

beingr the mosteflicient, which prism a is preferably formed by cutting one end of a short glass rod b at an angle of about fortyv five degrees to the axis and grinding the sides a and faee-al flat, though this is not indispensable. The reflectingsurfaee a"L is polished', and the sides and face of the prism or y the glass rod round the end cut at an angle are preferably ground dull, so as to diffuse the light falling upon the reflecting-surface a, and the glass rod beyond the prism is coated4 with black or inelosed in a tube c to exclude other light. At the other end of the glass rod a lenticular surface or lens d may be formed, as shown by Figs. 2 and 3, the focus of the lens beingat or about the center of the reflect in g-sn rface a, or instead thereof a lens d', Fig. 4, may be fixed in the end of a tube c, sliding in the tube e, into which the glass rod b, which in this case is made shorter and cut square at the end, is inserted, so that the surface a can be accurately focused.

The object of the lens or lenticular surface is to magnify the crystals inspected through the instrument, and the end of the glass rod may be cut and polished flat and square to the axis if the crystals to be tested are suffi eiently large not to require magnification.

In order to test a crystal f with an instrument constructed as hereinbefore described, one of its facets is placed directly against the polished inclined surface ui, Inoistened pre viously with a little liquid, preferably with one having a high refractive index, such as I cedar or cassia oil, but water will su tlice when ow as the refract Ive power of the diamond the user is accustomed to the instrument. III ease the crystal is a diamond considerable light will be seen reflected from the facet touching the prism, and when viewing it through the lenticular end of the instrument the facet will be very distinctly seen, showing brightly with sharp outlines, whereas if the crystal is paste or other suhstance'used in imitation of diamonds the facet will be scarcely distinguishable fronrthe surrounding mediumrin which it is immersed and appear without any distinct outlines.

l claim as my invention- A l. \n optical instrument for testingr dia- Inonds, consisting of the combination of a to tallyretleeting prism, a tube of opaquematcrnl extending from one of the side faces of tube, said icns being adjxistabie to and from the prism, and a nmgnfying-lens within the the prism.

tube. In testimony whereof I have hereunto set J An optical instrumentfor testing diamysignnt-ureinthepresence of twowtnesses. monds, consisting of the combination of a to- THOMAS THORP. tnlLv-reecting prism, n. tube of opaque ma- \Vitnesses: I terinl extending from one of the side faces of R. J. URQUHARTL l the prism, and a nmgnii'ying-l'ens within the CARL BOLLE. 4I. a i f d P 4:a

Y A s A r. l f i l *W4* m3rduv*J-W" 4M; 1 -Avuiwm,...,...,,:..M,.-.;m.ww-twgi J 

